"Biochips" or arrays of binding agents, such as oligonucleotides and peptides, have become an increasingly important tool in the biotechnology industry and related fields. These binding agent arrays, in which a plurality of binding agents are deposited onto a solid support surface in the form of an array or pattern, find use in a variety of applications, including gene expression analysis, drug screening, nucleic acid sequencing, mutation analysis, and the like.
In array-based assays in which an array of binding agents is employed, the array is typically contacted with a fluid sample that is suspected of containing the analyte(s) of interest. In currently employed protocols, contact of the array with the sample fluid is achieved in a number of different ways. Thus, a fluid sample may be contacted with the surface of the array using a pipette. In other embodiments, the sample may be flowed over the surface of an array by injecting the sample through a septum. In yet other embodiments, the sample may be flowed over the surface of the array using surface tension, centrifugal force or pressure differentials.
Although effective, there are drawbacks associated with each of the above techniques. First, each of the above techniques requires the deposition of relatively large sample volumes, e.g. greater than 2 .mu.l. Second, such techniques provide little or no spatial resolution of sample presentation. Third, sample pre-manipulation or pre-treatment, e.g. heating, dilution, etc., is difficult.
As such, there is continued interest in the development of new methods of depositing sample volumes onto array surfaces. Of particular interest would be the development of a sample deposition method capable of depositing relatively small quantities of sample on the array surface in a manner in which the position of deposition can be controlled.